1. Field of the Invention
The present invention relates to a battery comprising at least a positive electrode, a negative electrode and an electrolyte as composing elements, and to battery electrodes therefore, and more particularly, to the battery having nitroxyl radical compounds as a active material of the positive and/or the negative electrode, high energy density and excellent stability, and to electrodes suitable to form the battery such as this.
2. Description of the Related Art
A battery is a device which can take out chemical energy as electric energy utilizing oxidation-reduction reactions occurring on a positive electrode and a negative electrode or can store electric energy as chemical energy, and is utilized as a power source in various equipment.
Recently, with the spread of mobile electronic equipment, there have been increased needs for a lightweight battery with a large capacity. To satisfy the needs, a battery has been developed which utilizes alkali-metal ions whose mass per unit electric charge is light. Among others, a lithium-ion battery is particularly utilized for various mobile equipments for its superiority in stability and large capacity. The lithium-ion battery uses a heavy-metal oxide containing lithium as an active material in the positive electrode and a carbon electrode as an active material in the negative electrode respectively and charge and discharge are performed utilizing a reaction of lithium-ion insertion in and elimination from these electrodes.
However, since the lithium-ion battery utilizes a heavy-metal compound with large specific gravity particularly as an active material in the positive electrode, it has not a sufficient capacity per unit mass of the battery and there has been a problem that it cannot act as a battery having a high energy density.
Therefore, developments of a battery having a large capacity utilizing electrode materials having less weight have been tried. For example, U.S. Pat. No. 4,833,048 and Japanese Patent 2,715,778 have disclosed a battery using an organic compound having a disulfide bond as an active material in a positive electrode, which utilizes an electrochemical oxidation-reduction reaction based on formation and dissociation of the disulfide bond.
Since the battery utilizes organic compounds comprising elements having a smaller mass such as sulfur and carbon as electrode materials, these materials are effective to some degree in providing a battery with high energy density, however, there has been problems that the efficiency of rebinding of the dissociated disulfide bond is small and the stability of charge and discharge was not sufficient.
There has been suggested a battery utilizing an organic compound, as an active material, i.e., a battery utilizing a conductive polymer as an electrode material. This battery performs charge and discharge by doping and undoping reactions of electrolyte ions for the conductive polymer. The doping reaction as described herein is defined as a reaction of stabilizing excitons such as charged solitons and polarons generated by the electrochemical redox reaction of the conductive polymer by counter ions. On the other hand, the undoping reaction as described herein is defined as a reverse reaction of the doping reaction, that is, the reaction of oxidizing or reducing electrochemically the excitons stabilized by the counter ions.
U.S. Pat. No. 4,442,187 has disclosed a battery using the conductive polymer as a positive electrode material or a negative electrode material. Since the conductive polymer of the battery is composed of elements having a lower mass such as carbon and nitrogen, the development of a battery having a large capacity and a high energy density has been expected.
The conductive polymer, however, has a property in general that excitons generated by electrochemical redox reaction are delocalized over a wide region of π-electron conjugated system and interact each other, which causes a problem of limiting the concentration of excitons generated, and therefore, imposing restriction on the capacity of the battery.
Therefore, the battery which utilizes this kind of conductive polymer as an electrode material has been still insufficient from a view point of producing a battery having a large capacity although it has been effective in producing a lightweight battery.
As described above, it is impossible in principle to produce a battery having an energy density higher than existing ones by a lithium-ion battery utilizing a heavy metal oxide as an active material of positive electrode. There have been various proposals for a battery which utilizes a light mass compound as an active material of electrode in place of a heavy metal oxide having heavy mass, however, a battery having a high energy density with excellent stability has not been obtained yet.